/Engine/Source/Editor/UMGEditor/Public/WidgetBlueprintEditorUtils.h
static [TTuple](API\Runtime\Core\Misc\TTuple)< FVector2D, FVector2D > GetWidgetPreviewAreaAndSize ( [UUserWidget](API\Runtime\UMG\Blueprint\UUserWidget) * UserWidget, FVector2D DesiredSize, FVector2D PreviewSize, EDesignPreviewSizeMode ThumbnailSizeMode, [TOptional](API\Runtime\Core\IO\TOptional)< FVector2D > ThumbnailCustomSize )